Issue injecting network overlapping BGP next hop in bird6.

[Ondrej Zajicek]

On Fri, Dec 04, 2015 at 02:23:04PM -0800, João Taveira Araújo wrote:
> Hi,
> 
> I'm running into a difference in behaviour between bird and bird6,
> although admittedly it may come from netlink itself. I'm using bird
> 1.5.0, but have also tried with build from latest git head.
> 
> Assume a connection to an upstream router over a link addressed with
> 10.0.0.0/31 or AAAA::0/127 for IPv4 and IPv6 respectively. For IPv4,
> the upstream announces the follow prefix:
> 
> 10.0.0.0/31     via 10.0.0.0 on eth0 [session 22:14:01] ! (100)
>         BGP.next_hop: 10.0.0.0
> 
> In this case the route fails to be injected into the FIB, because a
> route already exists from proto kernel, as the interface is addressed
> from that prefix.
> 
> In IPv6, the same thing happens, but on restarting bird6 all routes
> fail to get injected, each with the following error: "Netlink: No
> route to host".

Hi

Thanks for the report. I guess that in IPv6, the AAAA::0/127 succeed to
be injected, because it has different metric (kernel added ones have 256
by default while userspace have 1024 by default), se there are two routes
afterwards, but when BIRD want to remove its route during restart, kernel
seems to ignore the protocol field of the route and remove the kernel
route instead of the BIRD route. Without the kernel route, kernel does
not allow routes with related next hop to be injected.

In IPv4, kernel checks protocol field and do not remove routes from
other protocols when one is specified.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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